Circuit arrangement with simplified input circuit for phase modulation in a backscattering transponder

Abstract

A circuit arrangement for phase modulation in an input circuit of a backscattering transponder includes a varactor and at most one capacitor connected in series between two antenna terminals, as well as a varactor control arrangement applying a control voltage to the varactor to selectively vary the capacitance thereof. One of the antenna terminals is connected directly to one of the varactor terminals without a capacitor therebetween. The other antenna terminal is connected either directly or through a capacitor to the other varactor terminal. One antenna terminal and/or one varactor terminal can be grounded. A DC-decoupling capacitor can be connected between a transponder circuit unit or a circuit ground and the common junction of the antenna terminal with the varactor terminal. The circuit arrangement is simple, economical, and uses minimal chip area by omitting further capacitors between the antenna terminals.

1. A phase modulating backscattering transponder comprising a circuit arrangement for varying an input impedance of an input circuit of said backscattering transponder to produce a phase modulation of a backscattered signal, said circuit arrangement comprising:
 first and second antenna terminals in the input circuit in order to connect an antenna thereto; 
 a varactor that has first and second varactor terminals by which said varactor is connected between said first and second antenna terminals in the input circuit; 
 a varactor control arrangement connected to at least one of said varactor terminals in order to apply a variable control voltage to said varactor so as to vary a capacitance of said varactor to thereby vary the input impedance and produce the phase modulation of the backscattered signal; and 
 zero or at most one capacitor connected in series with said varactor between said first and second antenna terminals. 
 
     
     
       2. The backscattering transponder according to  claim 1 , wherein said circuit arrangement does not include any capacitor connected in series with said varactor between said first and second antenna terminals. 
     
     
       3. The backscattering transponder according to  claim 2 , wherein said first and second antenna terminals are respectively connected directly to said first and second varactor terminals. 
     
     
       4. The backscattering transponder according to  claim 1 , including said one capacitor connected in series with said varactor between one of said varactor terminals and one of said antenna terminals, and having another of said antenna terminals connected directly to another of said varactor terminals. 
     
     
       5. The backscattering transponder according to  claim 1 , further in combination with said antenna, which is a closed loop antenna. 
     
     
       6. The backscattering transponder according to  claim 1 , further in combination with said antenna, which is an open non-loop antenna. 
     
     
       7. The backscattering transponder according to  claim 1 , wherein one of said antenna terminals is connected to a reference voltage. 
     
     
       8. The backscattering transponder according to  claim 7 , wherein said reference voltage is a circuit ground of said circuit arrangement. 
     
     
       9. The backscattering transponder according to  claim 7 , wherein one of said varactor terminals is connected directly to said one of said antenna terminals that is connected to said reference voltage. 
     
     
       10. The backscattering transponder according to  claim 1 , further comprising a decoupling capacitor connected between one of said antenna terminals and a reference voltage. 
     
     
       11. The backscattering transponder according to  claim 10 , wherein said reference voltage is a circuit ground of said circuit arrangement. 
     
     
       12. The backscattering transponder according to  claim 10 , wherein said one of said antenna terminals is connected directly to one of said varactor terminals. 
     
     
       13. The backscattering transponder according to  claim 1 , further comprising a transponder circuit unit connected directly or indirectly to one of said antenna terminals. 
     
     
       14. The backscattering transponder according to  claim 13 , wherein said transponder circuit unit comprises at least one of a rectifier and a symbol recovery circuit. 
     
     
       15. The backscattering transponder according to  claim 13 , further comprising a decoupling capacitor connected between said one of said antenna terminals and said transponder circuit unit. 
     
     
       16. The backscattering transponder according to  claim 15 , wherein said one of said antenna terminals is connected directly to one of said varactor terminals. 
     
     
       17. The backscattering transponder according to  claim 13 , wherein said transponder circuit unit is connected directly to said one of said antenna terminals. 
     
     
       18. The backscattering transponder according to  claim 17 , wherein said one capacitor is connected in series with said varactor between one of said varactor terminals and said one of said antenna terminals that is connected directly to said transponder circuit unit. 
     
     
       19. The backscattering transponder according to  claim 13 , wherein said transponder circuit unit incorporates a decoupling capacitor by which said transponder circuit unit is connected to said one of said antenna terminals. 
     
     
       20. A phase modulating backscattering transponder comprising a circuit arrangement for varying an input impedance of an input circuit of said backscattering transponder to produce a phase modulation of a backscattered signal, said circuit arrangement comprising:
 first and second antenna terminals in the input circuit in order to connect an antenna thereto; 
 a varactor that has first and second varactor terminals by which said varactor is connected between said first and second antenna terminals in the input circuit; and 
 a varactor control arrangement connected to at least one of said varactor terminals in order to apply a variable control voltage to said varactor so as to vary a capacitance of said varactor to thereby vary the input impedance and produce the phase modulation of the backscattered signal; 
 wherein said first antenna terminal is connected directly to said first varactor terminal with no capacitor therebetween. 
 
     
     
       21. The backscattering transponder according to  claim 20 , wherein said second antenna terminal is connected directly to said second varactor terminal with no capacitor therebetween. 
     
     
       22. The backscattering transponder according to  claim 20 , further comprising a capacitor connected in series with said varactor between said second antenna terminal and said second varactor terminal. 
     
     
       23. A circuit arrangement adapted to vary an input impedance of an input circuit of a backscattering transponder to produce a phase modulation of a backscattered signal, said circuit arrangement comprising:
 first and second antenna terminals in the input circuit in order to connect an antenna thereto; 
 a varactor that has first and second varactor terminals by which said varactor is connected between said first and second antenna terminals in the input circuit; 
 a varactor control arrangement connected to at least one of said varactor terminals in order to apply a variable control voltage to said varactor so as to vary a capacitance of said varactor; and 
 exactly one capacitor connected in series with said varactor between one of said varactor terminals and one of said antenna terminals which is further connected to a reference voltage. 
 
     
     
       24. A circuit arrangement adapted to vary an input impedance of an input circuit of a backscattering transponder to produce a phase modulation of a backscattered signal, said circuit arrangement comprising:
 first and second antenna terminals in the input circuit in order to connect an antenna thereto; 
 a varactor that has first and second varactor terminals by which said varactor is connected between said first and second antenna terminals in the input circuit; 
 a varactor control arrangement connected to at least one of said varactor terminals in order to apply a variable control voltage to said varactor so as to vary a capacitance of said varactor; and 
 a decoupling capacitor connected between a reference voltage and one of said antenna terminals that is connected directly to one of said varactor terminals; 
 wherein said circuit arrangement does not include any capacitor connected in series with said varactor between said first and second antenna terminals.